Cable terminal for ignition systems



June 26, 1962 Filed Aug. 24, 1960 A. T. H. FONTAINE CABLE TERMINAL FOR IGNITION SYSTEMS 3 Sheets-Sheet 1 I, v/l,

ATTY.

June 26, 1962 Filed Aug. 24, 1960 A. T. H. FONTAINE 3,041,498 CABLE TERMINAL FOR IGNITION SYSTEMS .3 Sheets-Sheet 2 INVENToR.-

AT. H FUNTAINB.

June 26, 1962 A. T. H. FONTAINE CABLE TERMINAL FOR IGNITION SYSTEMS 5 Sheets-Sheet 3 Filed Aug. 24, 1960 FIG.3.

INVENTOR: Afl". HFUNTAINE.

ATTYI United safes Patent o 3,041,498 CABLE TERMINAL FOR IGNITION SYSTEMS Antoine T. H. Fontaine, 12a Dr. Zamenhofstraat,

Rotterdam, Netherlands Filed Aug. 24, 1960, Ser. No. 51,737

Claims priority, application Netherlands Aug. 29, 1959 6 Claims. (Cl. 315-54) may -be present in any conductors within range of the ap-` paratus, and speciiically those generated by ignitionsystems during the sparking action.

It is well known that the voltage waveY in a spark plug conductor increases rapidly until the spark gap is broken down and Ilthen decreases rapidly. As this Wave 'is not sinusoidal but rich in the higher harmonics, these higher frequency components generated are picked up by adjacent radio receiving apparatus. The harmonics produce in the receiver unitsv a. sputtering sound sufficient to seriously interfere withradio reception.

Heretofore suchmethodsas shieldingthe entire engine or only the ignition system have been tried and these methods have proved too inconvenient and bulky. Also filter systems have been used, these systems necessitating special coils and condensers which increase the weight of the motor element and the space required per horse power.

The present invention combines the effectiveness of the shield and filter methods with substantially no change in Weight, space and convenience from the ordinary ignition wiring system.

In one embodiment the invention provides a cable termination for ignition systems providing a high degree of protection against the disturbances discussed and commonly occasioned by sparks in the ignition system. The frequency region concerned is particularly that about 40 megacycles, being the important region in connection with radio and television traic.

It is one object of the invention to construct this cable termination from. coil sections in such a manner as to constitute series capacities in the relevant frequency range by inserting the entire coil in a screen of attenuating material such as ordinary plain commercial thin plate iron, with respect to which the sections possess partial natural capacities resulting in a filter made up of 1r sections having practically no direct current resistance and functioning as connection between the end of the cable and a conductor terminating in a spark gap as used in ignition systems.

It is a feature of the invention to provide the termination in connection with spark gaps in sparking plugs of internal combustion engines.

It is another feature of the invention to provide the termination in connection with spark gaps occurring in a distributor of an ignition system.

The filter is active above its resonance frequency as a capacitive voltage divider for the suppression of interference.

It is an object of the invention to suppress interference from the operation of systems involving spark discharges by providing a material at a definite point which attenuates by eddy current losses currents induced by spark discharges in an extensive system.

It is another object of the invention to provide an interference suppressor of the type considered in the shape of a plurality of current sections in series relation in an absorbing sleeve such as to constitute a vrm lilter for insertion at a definite point adjacent a spark gap.

A better understanding of the invention will be had from the detailed description to follow, in connection with the attached drawing in which FIGURE l is a viewof the screening of a spark plug in a first embodiment of a filtering cable terminal obtained by building coil sections into a cap for a sparking plus;

FIGURE Z is the basic form of the iilter;

FIGURE 3 is a lter diagram;

FIGURE 4 is a family of curves characteristic for the action of the iilter of FIG. 3;

FIGURE 5 is an idealized curve taken from this family;

FIGURE 6 is a diagram illustrative of the action of the filter of FIG. 3 above the resonance frequency of FIG. 5;

FIGURE 7 is a section of a practical suppressor with shield as shown in FIG. 1; and

FIG. 8 is a sectional view taken along line VIII-VIII of FIG. 7 with a part broken away.

The invention initially considers a normal metallic spark plug cap with extended nozzle as shown in FIG. 1 and consisting of a shell ,1 fitting closely cna spark plug and having a nozzle Z enclosing a pin 3; clamping the spark plug conductor or cable C.V

The spark cable C is connected to the pin 3` by pressing the cable into the nozzle (see also FIG. 7).

I have found that the suppressing effect of a normal metal plug cap in itself is quite small, for which reason I provide filter sections by replacing the direct connection between the pin 3 and the plug conductor by a coil 5 (see FIG. 7) made up of sections and having practically no resistance. The sections all lie within the screening shell 1, with regard to which they present natural capacities, resulting in the presence in the connection from the cable to the spark gap, of a low-pass lter made up of rm sections.

The basic form of this low-pass filter is shown in FIG- URES 2 and 3, whereas FIG. 4 `gives an extract from a family of curves for these filters showing the region irnportant for the present purpose, mainly consisting of suppression in the region between 40 and 240 megacycles, though it is also active at higher frequency, at least up to 800 megacycles, compare FIG. 6 showing the basic form of the same filter at higher frequency.

Moreover the lter also has a suppressing action at higher radio frequencies below 40 megacycles.

FIG. 4 shows the attenuation in decibels db as a function of the normalized or resonant frequency with the quantity m` (i.e. the ratio of series and shunt capacities) as parameter. The quality Q of a coil section is supposed to be infinite. In a practical case Q will be small resulting in the dotted graph.

FIG. 5 shows the behaviour of the lter.

FIG. 7 shows a section of a plug cap according to the invention in two mutually orthogonal directions, showing at 1 the lug shell over a spark plug P, at 2 the nozzle, at 3 the conducting pin protruding from the nozzle 2 to contact the cable C core W, at 4 the clamp for gripping the plug conductor, at 5 the coil wound on a grooved cylinder 6 of refractory insulation and at 7 the insulating body in the shell supporting the internal parts and the coil.

It is ya feature that the provision of the subtle means described at the relevant point in the ignition circuit constitutes an eiective suppression by repeated voltage division in consecutive sections, each of which in itself only provides small attenuation.

Patented June 26, 1962 It will be understood, of course, that the disclosure herein has been to a particular means for carrying out the invention, but the appended claims are intended to co-ver such equivalent combinations as the state of the art will allow.

What is claimed is:

1. In anignition system `for internal combustion engines having (A) a Spark plus,

(B) a source for energizing said plug,

(C) a conductor between said plug and said source,

and

(D) an element for `absorbing parasitic frequencies from the sparks produced by said plug, said element being connected between said plug and said conductor and comprising:

(l) a series of coil sections with low `direct current resistance, `and (2) a grounded metallic sheath having inherent losses surrounding said coil,

`said element constituting:

(a) a capacitive voltage divider in a range of interference frequencies above the resonant frequency of said coil sections, by reason of the capacitance of said coil sections in axial valignment and of the distributed capacitance of said coil sections with respect to said metallic sheath, and

(b) an mderived low pass lter having coil sections of low quality at frequencies below resonance of said element.

2. An element according 4to claim 1 wherein said coil comprises an insulated cylinder having spaced circumferential grooves therealong each of which contains a coil section.

3. An element according to clai-m 1 wherein said grounded metallic sheath is grounded Iby being connected to the outside of said spark plug.

4. A cable terminal yfor absorbing parasitic frequencies yfrom spark gaps comprising:

(a) a sectionalized series coil with low direct current resistance;

(b) a grounded metallic sheath having inherent losses `surrounding said coil; Y

said coil and sheath constituting, in a range of frequencies `above the resonant frequencies of the coil sections, a capacitive voltage divider by reason of the capacitance of the coil sections in longitudinal branches and of the distributed capacitance of the coil sections with respect to said metallic `surrounding sheath, which `at frequency below resonance acts as yan m-derived low pass ilter having coil sections of low quality.

5. A terminal according to claim 4 in which the natural resonant frequency of said sectionalized coil lies f-below the lowest frequency of fthe suppression region.

6. A terminal according to claim 4 wherein said coil comprises an insulated cylinder having spaced circumferentially grooves each of which contains a coil section.

References Cited in the file of this patent UNITED STATES PATENTS 1,971,497 Miller Aug. 28, 1934 2,173,766 Ramsay Sept. 19, 1939 2,350,367 Peters et al. June 6, 1944 

